A new magnetic solid acid catalyst was synthesized by immobilizing an ionic liquid precursor obtained from (3-aminopropyl)trimethoxysilane onto a magnetic core. The magnetic solid acid catalyst has a core shell structure, and the acid sites on the shell were easily accessible to reactants. The catalytic activities of the magnetic solid acid were investigated by biodiesel synthesis from waste oils. The solid acid exhibited a higher activity than traditional acid catalysts and the ionic liquid precursor. The core-shell structure and magnetic attraction between the particles provided strong ionic interactions, resulting in the high activity and stability. The main characteristics of the magnetic solid acid catalyst were as follows: easily accessible acidic sites, simple magnetic separation and high waste oil utilization. (C) 2016 Published by Elsevier Ltd.